This invention relates in general to the construction of drills and, in particular, to a new and useful hammer drill in which a percussion body is driven by a reciprocating piston through an intermediate pneumatic buffer zone, and a cylinder, forming the space for the movement of the percussion body and piston and the buffer zone, includes a collar, which is held between the housing parts, and is provided with air passages therethrough which communicate the interior of the cylinder with an air passage surrounding the cylinder in the housing which is sealed from adjacent components of the housing and from the ambient atmosphere.